Transport In Tubes Research Articles

Baryon transport in color flux tubes

Baryon transport in color flux tubes

Interactions between elementary waves and weak discontinuity in two-layer blood flow through artery

Blood flow through arterial circulation can be characterized by fluid transport in flexible tubes and modeled mathematically using the conservation of mass and momentum. A one-dimensional model for two-layer blood flow with different blood velocities and the same constant density in each layer derived from the Euler equations of gas dynamics by taking the vertical average across each layer. This work presents interactions of elementary waves with a weak discontinuity for the quasilinear 3 × 3 system of conservation laws governing the two-layer blood flow in arteries. Exploiting elementary waves as a single-parameter curve, we study the Riemann solution uniquely and consequently establish the condition on initial data for the existence of a solution to the Riemann problem. Furthermore, we discuss the evolution of weak discontinuity waves and subsequently derive their amplitudes; in what follows, we investigate the interactions of weak discontinuity with contact discontinuity and shocks. Finally, a series of numerical tests have been performed to understand the impact of shock strength and the initial data on the amplitudes of reflected and transmitted waves and the jumps in shock acceleration.

Improvement in the simulation tools for heat distribution predictions and control of baffle and middle divertor loads in Wendelstein 7-X

In the first divertor campaign in Wendelstein 7-X (W7-X), unexpected significant heat loads were observed at particular plasma-facing components (e.g. baffle tiles and middle divertor part) which were not designed to receive high heat flux. In a prior investigation, it was concluded that the previous diffusive field line tracing (DFLT) model used for divertor design in W7-X cannot reproduce these loads, due to the missing physics in simulating the heat transport in the shaded flux tubes. To tackle this issue, two new efficient codes (DFLT_rev and EMC3-Lite) are introduced and validated against various experimental heat distributions in different magnetic configurations. The new tungsten baffle tiles have been designed with these codes and mounted in the machine, aiming for mitigated heat loads in the upcoming campaign.

Modeling electron transport and multiplication in photomultiplier tubes using COMSOL Multiphysics®

Combining stochastic and finite element methods, a modeling approach was executed that will inform new photomultiplier tube and scintillation detector designs. Time-dependent signal formation within a commercially available photomultiplier tube was modeled including the release and transport of electrons from the photocathode through the dynode stages. An ET Enterprises 9214B photomultiplier tube was digitally reproduced using Computed Tomography, X-ray radiography, and SolidWorks solid-modeling software. Simulations were executed with COMSOL Multiphysics® finite element solving package. Stochastic models of electron emission from the photocathode and dynodes were integrated within the COMSOL framework. Photoelectron emission energy was modeled by combining NaI(Tl) spectral emission characteristics and K2CsSb photocathode quantum efficiency. Secondary electron emission yields were produced to follow nominal photomultiplier gain, while secondary electron energies were sampled from the Chung-Everhart distribution. Electron emission trajectories were sampled according to Lambert's cosine law. Coupling stochastic and finite element models, simulation reproduced signal formation for the commercial photomultiplier tube including timing characteristics within 9.5% and gain within 3% over a voltage range of 900–1250 V.

Not T too! False elevations in high-sensitivity cardiac troponin T (hs-TnT) following specimen transport

Though false elevations attributed to preanalytical specimen handling have been widely reported for Troponin I (TnI), Troponin T (TnT) has appeared more robust to falsely elevated Tn. We describe reproducible false elevations in high sensitivity TnT (hs-TnT) in specimens after courier transport in plasma separator tubes (PST) off-site for testing.Hs-TnT was measured under 5 different conditions: 1) at collection location (N = 24); 2) after transport upright in racks (N = 66); 3) after transport with no control over tube agitation (N = 69); 4) on transported aliquots (N = 84); or 5) immediately after transport with no control over tube agitation (N = 16), followed by keeping the specimen upright and re-measuring at 1hr, 2hr, 4hr, and 20-24hrs (N = 6). To assess the degree of discrepancy, plasma from the original PST was aliquotted, re-centrifuged, potential debris removed, and hs-TnT re-measured.43% of PST specimens collected offsite and transported with no control over tube agitation had clinically significant false elevations of hs-TnT which subsequently decreased following aliquotting and re-centrifugation (median decrease = 9.9 ng/L). Onsite testing or transported aliquots demonstrated no discrepancy. After being kept upright, discrepant specimens were not different from re-centrifuged aliquots by 4hrs (p = 0.6141, repeated measures ANOVA with Dunn’s multiple comparisons).Clinically significant false elevations of hs-TnT occurred in approximately 40% of separated PSTs that were transported in containers where specimens are transported with no control over tube agitation. This interference does not occur if plasma is aliquoted or if hs-TnT is tested at the collection site. In order to prevent these false elevations, and their potential patient impact on the diagnosis of acute myocardial infarction, specimens for hs-TnT measurement should be aliquoted at the collection location prior to transport.

Approximations of the extended Graetz problem to quantify particulate matter transport and deposition in tubes

Two different analytical solutions of the extended Graetz problem are analyzed in order to quantify the dynamics of particulate matter (PM) in a cylindrical element. Advection, diffusion and deposition of particles are calculated in a symmetrical circular tube with fully developed laminar flow applying the theory of confluent hypergeometric functions. The following in silico experiments are proposed: (i) the simulation of a thin tube deposition, acting as a filtering element for PM and (ii) the modeling of isokinetic sampling in the inner region of the tube. Two mathematical formulations are compared to obtain the general analytical solution of the advection-diffusion equation in cylindrical coordinates. After applying the variable separation method, a second order ordinary differential equation (ODE) is obtained, this ODE is solved with two distinct forms: (a) applying a transformation of variables to Whittaker’s function and (b) using a new variable transformation proposition. No studies were found that compare these analytical solutions, as well as the use of this new variable transformation, although both cases are essentially different ways of applying the Frobenius method. In this work, 75 eigenvalues and their constants are presented for the first time using five decimal places. The new series solution has high accuracy compared to the previous one, it can provide the concentration profile, the deposition rate and the determination of the PM profile in the isokinetic sampling region. Our solution proved to be more stable close to the tube wall, which may improve the techniques for measuring the flow of particles in tubes. Furthermore, using more eigenvalues improved the estimation of PM2.5 and PM10 deposition. The results presented here show that the proposed new analytic solution has the potential to contribute to numerical and experimental environmental analyses.

Analysis of slip effects on slow viscoelastic flow of second order fluid through a small diameter permeable tube

There are various models which describe the hydro-dynamical aspects of the fluid flow and solute transport in small diameter permeable tubes without incorporating the slip effects, which play an important role to predict the flow behavior with higher accuracy. This study aims to investigate the slip effects on the slow, steady-state and axisymmetric flow of an incompressible second order Rivlin–Ericksen fluid in a small diameter cylindrical tube with constant wall permeability. The momentum equations have been derived in cylindrical coordinates and are converted in the form of a single compatibility equation which governs the stream function of the flow. Navier slip condition has been used to take slip phenomenon into account near the wall of the tube. Compatibility equation has been solved analytically subject to the associated boundary conditions by using Langlois recursive approach method. The detailed expressions have been obtained for velocity components, pressure, volume flow rate, pressure drop along longitudinal axis, wall shear stress, fractional reabsorption and leakage flux. Behavior of all the flow variables against the slip parameter has been examined graphically in detail. Overall, the solutions obtained her e show a great agreement with the work in literature. One of the key findings in this study is that the volume flow rate Q is found to be independent of the slip parameter ϕ.

Novel Control-Oriented Models for Liquid Transport in Falling Film Evaporator Tubes

The paper presents novel control-oriented transport models for evaporating liquid films in the tubes of a falling film evaporator. In this context, our goal consists in qualitatively mapping the experimentally observed input-output behavior. Two transport models are proposed, where the difference between them is that one allows overtaking of liquid particles and the other does not. The transport models are equipped with two new models of evaporation which are different from the commonly assumed uniform evaporation. The models are initially developed from the conservation laws in the form of partial differential equations. Using the method of characteristics we then obtain the input-output relations for the proposed models in the form of time-delay equations. The time-delay representation is advantageous for simulation and for the future control design. In a simulation study, we observe the principal properties of the models and find that they correspond well with the experimentally observed input-output behavior.

Crystal structure and physical properties of Ba2Nb3S8I: A new misfit-layered transition-metal dichalcogenide superconductor

Single crystals of Ba2Nb3S8I have been grown using iodine-vapor transport in fused-quartz tubes. The crystals form as flakes with typical areas of 5–10 mm2 and thicknesses of 5–11 μm. The crystal structure was determined using single-crystal x-ray diffraction with the aid of an APEX II CCD diffractometer. The structure shows trigonal symmetry with space group P31c and lattice parameters a = b = 10.0156(5) Å and c = 25.1414(15) Å. Compositional analysis via x-ray spectroscopy confirms the presence of iodine. Superlattice reflections are evident in x-ray precession images. Measurements of the electrical resistivity reveal a metallic temperature dependence and superconductivity near 1 K. Polycrystalline samples of Ba2Nb3S8I were made in order to have samples large enough for other bulk physical properties measurements. Magnetic susceptibility reveals antiferromagnetism below 275 K. The coexistence of antiferromagnetism and superconductivity is surprising. Specific heat measurements reveal the electronic coefficient γ = 3.95(66) mJ/mol K2. The jump in the specific heat at the superconducting transition temperature Tc (ΔC/γTc = 1.4(2)) and the energy gap associated with the superconducting state (Eg = 0.405(17) meV) agree well with BCS theory.

Aerosol deposition in circular tubes with simultaneous consideration of diffusion and sedimentation

Aerosol deposition from laminar flow in a horizontal circular tube is studied analytically considering the combined mechanisms of Brownian diffusion and gravitational settling, and the mean concentration and deposition velocity are calculated and analyzed by using the theoretical solution. The results show that when both diffusional and gravitational effects are considered, the deposition velocity varies non-monotonically with respect to transport distance in the tube. This is different from that of deposition by diffusion alone. For the case when the gravitational effect is negligible, aerosol convective transport in tubes is compared with existing results, and the analysis indicates that the results in the literature dealing with this aspect can be determined by simplifying the present solution under specific conditions. The comparisons of mean concentration due to pure diffusion and combined mechanisms between the previous studies and the present results also indicate that the explicit general solution of this study can be used to describe aerosol deposition at any distance in a horizontal circular tube.

Beam Transport and Beam-Current Loss in Emittance-Dominated High-Frequency Tubes

Emittance effects are becoming increasingly important in high-frequency electron devices, especially in recent and proposed high-frequency traveling wave tubes and klystrons. The ratio of beam radius to the beam pipe, typically referred to as “fill factor,” is a critical parameter for high-frequency tubes. Fill factors, typical of lower frequency tubes, such as 0.5–0.8, can lead to significant beam current loss in high-frequency tubes when transported over long distances in the beam pipe because the beam in such tubes is more subject to emittance effects. The increased beam loss, in turn, leads to large dissipation of beam power at the RF circuit, damaging the circuit itself and limiting tube’s duty cycle. Traditionally, the beam emittance has been largely studied and measured in linear accelerators (linacs) where emittance effects are larger than space-charge effects at high beam energy. In this paper, we apply the beam physics developed for linacs to high-frequency tubes for the first time. We provide necessary theoretical tools to determine the fundamental limit of the beam pipe sizes for a desired limit of beam interception. Specifically, the effect of both space charge and emittance is incorporated into iterative solution of equilibrium distributions of charge densities in the presence of a uniform focusing axial magnetic field. The numerical solutions and tools provided here can be used to determine the beam pipe size for any beam emittance. The theoretical formulation and results are expected to be particularly useful for devices operating from mm-wave to subterahertz frequency regimes.

A simple method for mitochondrial respiration and calcium uptake assessment in pollen tubes

Key mitochondrial processes are known to be widely conserved throughout the eukaryotic domain. However, the scarce availability of working materials may restrict the assessment of such mitochondrial activities in several working models. Pollen tube mitochondrial studies represent one example of this, where tests have been often restricted due the physical impossibility of performing experiments with isolated mitochondria in enough quantities. Here we detail a method to measure in situ mitochondrial respiratory chain activity and calcium transport in tobacco pollen tubes.•Digitonin-mediated plasmalemma permeabilization allows efficient assessment of mitochondrial respiration and calcium uptake.•This method allows quick, reliable and portable measurements from low to high cellular densities, versus methods requiring intracellular calcium reporters.

Metal-Air Transistors: Semiconductor-Free Field-Emission Air-Channel Nanoelectronics.

Scattering-free transport in vacuum tubes has always been superior to solid-state transistors. It is the advanced fabrication with mass production capability at low cost which drove solid-state nanoelectronics. Here, we combine the best of vacuum tubes with advanced nanofabrication technology. We present nanoscale, metal-based, field emission air channel transistors. Comparative analysis of tungsten-, gold-, and platinum-based devices is presented. Devices are fabricated with electron beam lithography, achieving channel lengths less than 35 nm. With this small channel length, vacuum-like carrier transport is possible in air under room temperature and pressure. Source and drain electrodes have planar, symmetric, and sharp geometry. Because of this, devices operate in bidirection with voltages <2 V and current values in few tens of nanoamperes range. The experimental data shows that influential operation mechanism is Fowler-Nordheim tunnelling in tungsten and gold devices, while Schottky emission in platinum device. The presented work enables a technology where metal-based switchable nanoelectronics can be created on any dielectric surface with low energy requirements.

In situ assessment of mitochondrial calcium transport in tobacco pollen tubes

Pollen tubes require functional mitochondria in order to achieve fast and sustained growth. In addition, cell wall expansion requires a calcium gradient in the tube apex formed by a dedicated array of calcium pumps and channels. Most studies have traditionally focused on the molecular aspects of calcium interactions and transport across the pollen tube plasmalemma. However, calcium transients across mitochondrial membranes from pollen tubes are beginning to be studied. Here, we report the presence of a ruthenium red-sensitive mitochondrial calcium uniporter-like activity in tobacco pollen tubes with functional oxidative phosphorylation. The present study provides a framework to measure in situ specifics of mitochondrial transport and respiration in pollen tubes from different plants. The relevance of a mitochondrial calcium uniporter for pollen tube growth is discussed.

A computationally efficient pseudo-3D model for the numerical analysis of borehole heat exchangers

Ground-Source Heat Pump (GSHP) systems represent one of the most efficient renewable energy technologies. Their efficiency is highly influenced by the thermal properties of the ground, which are often measured in-situ using the Thermal Response Tests (TRTs). While three-dimensional mechanistic models offer significant advantages over analytical solutions for the numerical interpretation of TRTs, their computational cost represents a limiting factor. Moreover, most of the existing models do not include a comprehensive description of hydrological processes, which have proven to strongly influence the behavior of GSHP. Thus, in this study, we propose a computationally efficient pseudo-3D model for the numerical analysis and interpretation of TRTs. The numerical approach combines a one-dimensional description of the heat transport in the buried tubes of the exchanger with a two-dimensional description of the heat transfer and water flow in the surrounding subsurface soil, thus reducing the dimensionality of the problem and the computational cost. The modeling framework includes the widely used hydrological model, HYDRUS, which can simulate the movement of water, heat, and multiple solutes in variably-saturated porous media. First, the proposed model is validated against experimental data collected at two different experimental sites in Japan, with satisfactory results. Then, it is combined with the Morris method to carry out a sensitivity analysis of thermal properties. Finally, the model is exploited to investigate the influence of groundwater and lithologic heterogeneities on the thermal behavior of the GSHP.

An experimental study on particle effects in liquid sheets

Many industrial processes, such as surface coating or liquid transport in tubes, involve liquid sheets or thin films of suspensions. In these situations, the thickness of the liquid film becomes comparable to the particle size, which leads to unexpected dynamics. In addition, the classical constitutive rheological law for suspensions cannot be applied as the continuum approximation is no longer valid. Here, we consider experimentally a transient particle-laden liquid sheet that expands radially. We characterize the influence of the particles on the shape of the liquid film and the atomization process. We highlight that the presence of particles modifies the thickness and stability of the liquid sheet. Our study suggests that the influence of particles through capillary effects can modify significantly the dynamics of processes that involve suspensions and particles confined in liquid films.

Experimental study on evaporation from seasonally frozen soils under various water, solute and groundwater conditions in Inner Mongolia, China

Summary Soil freezing and thawing significantly impact water balance in cold regions. To improve estimations of evaporation from seasonally frozen and saline soils, field experiments representing various water and solute conditions were conducted during a 5-month-period in Inner Mongolia, China. A mass balance method was used to estimate evaporation from frost tubes (5.5 × 300 cm) with treatments combining three solute contents (0.2%, 0.4%, and 0.6% g g−1 dry soil) with three initial groundwater table depth (GWTDs) (2.0, 1.5, and 1.0 m). The dynamics of water, heat and solute transport in the frost tubes and in field plots were also investigated. Seasonal changes in evaporation rates were observed during soil freezing/thawing periods. Low evaporation rates were maintained when the soil was deeply frozen (e.g., in P3), and relatively higher values occurred at the beginning and the end of the experiments (e.g., in P1 and P5). The cumulative evaporation amount increased with an increase in initial solute content and declined with a lowering of the initial GWTDs. Solute accumulation with water in the surface layer during freezing decreased the osmotic potential in soil, resulting in obvious freezing point depressions and higher liquid water contents in the uppermost layer of soil. During the soil thawing periods, no evidence of any control of water availability on evaporation was noticed, although the surface soil contained large amounts of water. This study has led to an improved understanding of the coupled effects of water, heat and solute on evaporation from seasonally frozen saline soils and also has important implications for water and energy balance studies in cold regions.

Analytical and numerical investigation of the advective and dispersive transport in Herschel–Bulkley fluids by means of a Lattice–Boltzmann Two-Relaxation-Time scheme

Dispersion of a passive tracer in a tube has been extensively studied in the case of Newtonian fluids since the pioneer work of Taylor (1953). However, the influence of more complex rheological behavior on the transport has only be scarcely investigated. Non-Newtonian fluids are increasingly used in the industry and transport in this type of fluid merits therefore thorough investigations. An example of industrial application is Enhanced Oil Recovery, that is based on the injection of non-Newtonian fluids as polymers or surfactant solutions in porous media, which are then submitted to dispersion phenomena.This work deals with transport of a passive tracer in shear thinning fluids with and without yield stress whose constitutive behaviors are representative of a large number of industrial fluids. We focus on transport in capillary tubes, essential for the understanding of dispersion in porous media. Transport is investigated at different time scales by solving the advection–diffusion equation using a Two-Relaxation-Time Lattice–Boltzmann method. We also derived an analytical expression of the Taylor dispersion coefficient for a large range of fluid rheologies. Dispersion coefficients of all fluids described by the Herschel–Bulkley model can now be determined. Analytical and numerical results are compared and very good accordance is obtained.We discuss the characteristic time scales of the transport before reaching steady state as a function of fluid rheology and Péclet number. We show that the time to reach the dispersive regime is nearly independent of the fluid rheology whereas the effective dispersion coefficient is a function of the rheological parameters.We also present the displacement distribution of the tracer molecules (propagators) as a function of time and show that they are strongly conditioned by the fluid rheology. Indeed, propagators give valuable information on the temporal evolution of the concentration profile towards the stationary Taylor regime.

Aharonov-Bohm oscillations in a quasi-ballistic three-dimensional topological insulator nanowire.

Aharonov-Bohm oscillations effectively demonstrate coherent, ballistic transport in mesoscopic rings and tubes. In three-dimensional topological insulator nanowires, they can be used to not only characterize surface states but also to test predictions of unique topological behaviour. Here we report measurements of Aharonov-Bohm oscillations in (Bi1.33Sb0.67)Se3 that demonstrate salient features of topological nanowires. By fabricating quasi-ballistic three-dimensional topological insulator nanowire devices that are gate-tunable through the Dirac point, we are able to observe alternations of conductance maxima and minima with gate voltage. Near the Dirac point, we observe conductance minima for zero magnetic flux through the nanowire and corresponding maxima (having magnitudes of almost a conductance quantum) at magnetic flux equal to half a flux quantum; this is consistent with the presence of a low-energy topological mode. The observation of this mode is a necessary step towards utilizing topological properties at the nanoscale in post-CMOS applications.

Realizing one-dimensional quantum and high-frequency transport features in aligned single-walled carbon nanotube ropes

The superiority of the electronic transport properties of single-walled carbon nanotube (SWNT) ropes over SWNT mats is verified from low temperature and frequency-dependent transport. The overall change of resistance versus in nanotube mats shows that 3D variable range hopping is the dominant conduction mechanism within the 2–300 K range. The magneto-resistance (MR) is found to be predominantly negative with a parabolic nature, which can also be described by the hopping model. Although the positive upturn of the MR at low temperatures establishes the contribution from quantum interference, the inherent quantum transport in individual tubes is suppressed at elevated temperatures. Therefore, to minimize multi-channel effects from inter-tube interactions and other defects, two-terminal devices were fabricated from aligned SWNT (extracted from a mat) for low temperature transport as well as high-frequency measurements. In contrast to the mat, the aligned ropes exhibit step-like features in the differential conductance within the 80–300 K temperature range. The effects of plasmon propagation, unique to one dimension, were identified in electronic transport as a non-universal power-law dependence of the differential conductance on temperature and source-drain voltage. The complex impedance showed high power transmission capabilities up to 65 GHz as well as oscillations in the frequency range up to 30 GHz. The measurements suggest that aligned SWNT ropes have a realistic potential for high-speed device applications.